Treatment of wells



Patented June 6, 1939 warren STA-TE TREATMENT OF WELLS William Clifton Phalen, Syracuse, N. to The Solvay Process Company,

N. Y., a corporation of New York No Drawing. Application December 22 Serial No. 181,104

7 Claims.

This invention relates to treating wells for the production of fluids, such as oil, gas, water, etc. More particularly, it relates to treating wells in which the producing horizon is located in fine- 5 grained formations.

magnesium carbonate constituting thewalls of the drainage channels through the formation, and enlarges these channels.

Further, it has been proposed to treat wells with 20 an acid followed immediately by a limited quantity of alkali to neutralize the acid wetting the metal tubing of the well,,in order to avoid corrosion thereof, or to treat wells with alternate volumes of acid and alkali so that the acid and 25 alkali react within the. well to generate heat,

which is said to aid in opening the oil passageways.

However, notwithstanding the rapid strides which have been made in the development of oil 30 well treatment during the past few years, it is still well recognized that the desired degree of improvement in permeability is not always accom-. plished. While ordinary acid treatment may give satisfactory results when applied to wells located 5 in, one type of formation, it may be a commercial failure when applied to wells located in another type of formation. In fact, it has been shown' that an actual decrease in permeability may occur when fine-grained calcareous formations are 40 subjected to the same acid treatment successful in larger-grained formations. This decrease in permeability in fine-grained formations appears to be due to clogging of the small drainage chan-' nels by acid-insoluble residues. These insoluble 5 residues resulting from the acid treatment have been shown to be needle-like crystals of silicates mixed with a little colloidal silica and colloidal organic matter.

As might be expected, the clogging effect of the 5 acid-insoluble silicates and colloidal matter depends upon the size of the drainage channels;

i. e., the finer the drainage channels the greater the clogging effect and hence the greater the decrease inpermeability. Thus, in formations 5 where the drainage channels are very large and S PATENT OFFICE Y., assignor New York,

the fluids drain chiefly through the larger channels, such as in certain fields of north-central Texas and southeastern New Mexico, the acid may flow freely into enlarge them,

the large channels.- formations'such as many oil fields; for Lower the channels and further and any residue resulting from the acid treatment may be washed out through However, in fine-grained comprise the structure of instance, the Upper and Cretaceous limestone of Travis County,

Texas, and the Strawn sandstone in Palo Pinto County, Texas, the acid may flow only slowly through the formation, resulting from the acid granules and crystals and the silicious residue treatment may consist of larger than the fine drainage channels of the formation. As a result, some of the channels may permeability may be It is an object of become firmly clogged and decreased regardless of the amount of washing out that is attempted.

this invention to restore or increase the production of wells located in finegrained calcareous fo It is a further object rmations.

of this invention to supplement acid treatment of wells located in finegrained, calcareous formations with a chemical treatment which removes the acid treatment from the insoluble residue of the drainage channels invention comprises treatin fine-grained calcareous formations containing silicates first with acid, the acid being introduced into the well in the con-' ventional manner, and then,

after a sufilclent time has elapsed for substantially all of the acid to.react with the geological formation, with a solution of a hydroxide of an alkali-metal of the fine-grained formation.

suflicient strength and quantity to react with the s, which are formed by the which clog the channels in The alkali-metal hydroxide serves to convert the residues to soluble compounds,

whereby they are washed away and permeability is increased. Thus, contrary to prior treatments and alkali-metal. hy hydroxide of to neutralize therefrom.

involving the use of, both acid droxides, the alkali-metal my process does not serve merely the acid, but reacts with insoluble residues to the acidform soluble compounds The strength of the alkali-metal hydroxide solution employed may vary over wide limits; a

solution containing about NaOH by weight may be used. Concentrations above 10% are preferred over lower concentrations. The volume of alkali-metal hydroxide solution employed de- 'may be used. It is preferred to pumped into the well.

pends upon the amount .of acid-insoluble residue present in, and the size of, the area to be cleaned; in some cases a volume about one-half the volume of the acid used is sufficient. However, this value is in no way critical. It is to be understood that the principle involved is to dissolve the silicate residues resulting from the acid treatment and thus to increase the permeability of the formation; hence any quantity of alkalimetal hydroxide which performs this function is within the spirit of my invention. Where ample heating equipment is available, the alkali-metal hydroxide solution may be introduced into the well in a heated condition, say at a temperature around 100 C.

The particular acid chosen for use in my process will depend upon the nature of the formation. Any of the well known acid treatments use hydrochloric acid; however, other acids are suitable, as well as mixtures of acids; for instance, nitric acid or mixtures of hydrochloric and nitric acids form good treating agents for certain geological strata. The acid may contain a corrosion inhibitor.

The strength and quantity of acid used may vary widely; for instance, hydrochloric acid of from about 15% to about 36% HCl by weight may be used, and the quantity may vary from a few hundred to several thousands of gallons.

The time interval between introduction of acid' and introduction of alkali must be suflicient to accomplish the solution of a substantial amount of acid-solubles. The extent of reaction may be determined roughly by measuring the loss of acid concentration of the treating solution. Preferably, the time should be suflicient to substantially exhaust the acid; e. g., to reduce its concentration to 1% or less. Normally, an acid treatment period of from 10 to 24 hours is suflicient to accomplish the desired results. Under some circumstances, it

centrated fresh acid to the used acid, the solution may be placed in condition for reuse. method of operation is not feasible, however, unless the acid employed is available in substantially higher concentration than is desired for the treating solution.

The invention will be further illustrated by the following example, but it is to be understood that the invention is not limited thereto.

1000 gallons of hydrochloric acid containing 15% HCl by weight are pumped into an oil well located in a fine-grained limestone formation containing calcium and magnesium carbonates After the acid reacts for twenty-four hours the residual acid concentration is less than 1%. At this time, 500 gallons of a 10% caustic soda solution are The caustic soda reacts with the acid-insoluble silicate deposits which clog the drainage channels, to form a solution of soluble silicates. When the solution is removed from the formation, these silicates are washed out as are the calcium chloride, magnesium chloride, and other impurities. In this manner my process cleans the drainage channels and decidedly increases the permeability of the finegrained formation.

A wetting or penetrating agent may be added to the acid and alkaline treating solutions, if desired. In the case of alkaline solutions, the addition of a fraction of 1%, say 0.005% to 0.10%, of isopropylnaphthalene sodium sulfonate has been found to produce an especially beneficial increase in the penetration, thus shortening the time and increasing the effectiveness of the treatment.

I claim:

1. A process adapted for increasing the production of wells in acid-treated, fine-grained, silicate-containing, calcareous formations, which comprises introducing into the formation suflicient alkali-metal hydroxide solution to react with and dissolve a substantial proportion of the residue left by the acid treatment.

2. A process for increasing the production of and, after substantially introducing caustic soda tion.

5. A process for increasing the production of wells in fine-grained, silicate-containing, calcareat least 10 hours time has elapsed, about part by volume of aqueous caustic soda solution containing about 10% NaOH by weight into the formation to react with the acid-insoluble residue left by the acid treatment.

WILLIAM CLIFTON PHALEN.

introducing 

